IS 12672: 1969 hdian Standard ( Reaffirmed 2001 ) -\ I , INTERNALFUSESANDINTERNAL OVERPRESSUREDISCONNECTORSFOR SHUNT CAPACITORS-SPECIFICATION UDC 621'316'923 : 621'316'545 : 621'319'4'076-61 @ BIS 1990 . STANDARDS ZAFAR MARG Price Group 3 BUREAU OF INDIAN MANAK BHAVAN, 9 BAHADUR NEW DELHI March 1990 SHAH 110002 Power Capacitors Sectional Committee, ETDC 29 FOREWORD This Indian Standard was adopted by the Bureau of Indian Standards on 19 April 1989, after the draft finalized by the Power Capacitors Sectional Committee had been approved by the Electrotechnical Division Council. This standard is intended to formulate uniform requirements regarding performance, tests and provides guidance for the coordination of internal fuse and internal disconnector protection of the shunt capacitors covered in IS 2834 : 1986 `Specification for shunt capacitors for power systems ( second revision )`. The fuses and disconnectors conforming to this standard are designed to isolate faulted capacitor elements or capacitor units to allow operation of the remaining parts of that capacitor unit and the bank in which the capacitor unit is connected. Such fuses and disconnectors are not a substitute for a switching device, such as, circuit breaker, or external protection of the capacitor bank, or part thereof. This standard is based on the following publications/documents technical Commission ( IEC ): issued by the International fuses and Electrointernal a) IEC Pub 593 ( 1977 ) and Amendment No 1 ( April 1980 > Internal overpressure disconnectors for shunt capacitors, and b) Dot : 33 ( Central Office ) 72 Draft Amendment No. 2 to IEC Pub 593 ( 1977 ). IS 12672 : 1989 Indian Standard INTERNALFUSESANDINTERNAL OVERPRESSUREDISCONNECTORSFOR SHUNTCAPACITORS- SPECIFICATION 1 SCOPE 3.2 Bank Protection and guidance for coordination covers the requirements, tests of internal fuses used to protect shunt capacitors. 1.2 This standard also applies to internal overpressure disconnectors used to protect self-healing metallized dielectric capacitors. NOTE - The requirements of self-healing and nonself healing shunt capacitors for power systems are covered in IS 2384 : 1986 `Specification for shunt capacitors for power systems ( second revision )`. 1.1 This standard A general term for all protective a capacitor bank, or part thereof. 3.3 Internal Fuse equipment for A fuse connected inside a capacitor unit with an element or a group of elements. 3.4 Internal Overpressure in series Disconnector A disconnecting device inside a capacitor to interrupt the current rising pressure. designed path in case of excessive 1.3 This standard does not apply to fuses and disconnectors for which service conditions, in general, are not compatible with the requirements qf the standard, unless otherwise agreed to between the manufacturer and the purchaser. 1.4 The guidance for coordination of fuse and disconnector protection is given in Annex A. 2 REFERENCE 2.1 STANDARD NOTES 1 This overpressure disconnector is not a currentlimiting fuse. 2 This type of disconnector can also be placed outside the capacitor unit but is still considered an integral part of the capacitor unit. and shall fulfii the same iequirements &d pass the same tests as the internal overpressure disconnector. 3 This device is normally used in capacitors of the self-healing type. The following Indian Standards are necessary adjuncts to this standard. IS h'o. Title 3.5 Unbalance Protection IS 188.5 ( Part 42 ) : 1986 Electrotechnical sion ) IS 2834 : 1986 vocabulary: Part 42 Power capacitors (first revi- A device sensitive to capacitance difference between branches of the bank normally in talance with each other. The capacitance difference may be due to a blow fuse(s), or operation of a disconnector or insulation failure within the bank. NOTE - Other protective devices, such as, overcurrent and earth fault protection, are self-explanatory since they are commonly used for other applications. Specification for shunt capacitors for power systems ( second revision ) 4 GENERAL 4.1 REQUIREMENTS IS 9224 C in parts ) Specification voltage fuses for low high IS 9385 ( in parts ) 1S 9926 : 1981 Specification for voltage fuses Specification for fusewire used in rewirable type electric fuses up to 650 volts The fuse is connected in series to the element(s) which the fuse is intended to isolate if the element(s) becomes faulty. The range of currents and voltages for the fuse is, therefore, dependent on the capacitor design, and in some cases also on the bank in which the fuse is connected. 4.1.1 The operation of an internal fuse is in general determined by one or both of the following factors: a) The discharge energy from elements or units connected in parallel with the faulty element or unit, and 3 TERMINOLOGY 3.1 The following definitions in addition to those covered in IS 1885 ( Part 42 ) : 1986 shall apply. b) The power-frequency fault current. NOTE - The word `element' in this standard is used in accordance with definitions contained in IS 1885 C Part 42 ) : 1986 and not in accordance with IS 9224, IS 9926 : 1981or IS 9385. 4.2 The disconnector is intended to interrupt the current to all elements of the capacitor. The proper operation of the disconnector is dependent 1 IS 12672 : 1989 on the leak tightness of the container life of the capacitor. DISCONNECTING during the NOTE - The requirements are valid if the capacitors are switched by a restrike-free circuit-breaker. If the breakers are not restrike-free, other requirements are to be agreed between the manufacturer and the purchaser. 5 REQUiREMENTS 5.1 The fuse shall enable the faulty element to be disconnected when electrical breakdown of elements occurs in a voltage range, in which II, is the lowest, and U, is the highest (instantaneous) value of the voltage between the terminals of the unit at the instant of fault. 5.1.1 The recommended given in Table 1. values for U, and Uz are 6.3 The fuse and the disconnector shall be capable of withstanding the inrush-currents due to the switching operations expected during the life of the capacitor. 6.4 The fuse connected to the undamaged element(s) must be able to carry the discharge currents due to the breakdown of element(s). 6.5 The fuses and disconnectors must be able to carry the currents due to short-circuit faults extended to the unit(s) on the bank occurring within the voltage range in accordance with Table 1. 7 MARKING 7.1 5.2 The disconnector shall enable the faulty capacitor unit to be disconnected for voltages up to and including CT,. 5.2.1 The recommended NOTE - The purchaser will be exceeded. rms value is U3=1'2 UN. shall specify if this voltage Table 1 Recommended Value of U1 and U, ( Clauses 5.1.1 and 6.5 ) UI (Lower Limit) (2) o*g&tfN The marking regarding the presence of internal fuse and internal overpressure disconnector shall be provided on the rating plate of the shunt capacitor. 8 TESTS Rated Bank Vdltage (1) U, (Upper Limit) ( 3) 13&-UN 8.1 Type Tests Up to 650 V Above 650 V NOTES The following shall constitute a) Discharge test ( see 9 ); type tests: o*ss/F.rr, 2.0 &UN 1 The CJ,and U. values above are based on the voltage that may normally occur across the capacitor utiit terminals at the instant of electrical breakdown of the element. The U, values are of a transient nature and allowance has been made for increased damping at low voltage. The purchaser shall specify if the r/l and Up values differ from those given in Table 1. If SO, the values in Tables 3 and 4 shall be changed accordingly. a:e valid for a bank switched by a restrike-free circuit-breaker. If the breakers are not restrike-free, the other requirements shall be as agreed to between the manufacturer and the purchaser. b) Disconnecting test on fuses ( see 10 >; and c) Disconnecting test on disconnector ( see 11 >. NOTES 1 In addition to above requirements, the fuses and disconnectors shall be able to withstand all type tests of the capacitor units specified in IS 2834 : 1986. 2 Type tests of fuses are performed complete capacitor unit or, at the choice facturer, on two units, one unit being lower voltage limit, in accordance with unit at the upper voltage limit. The unit(s) shall have passed ail routine IS 2834 : 1986. 3 Due it may unit(s) Annex Annex 8.1.1 either on one of the manutested at the 10.1 and one tests stated in 2 The requirements 6 WITHSTAND REQUIREMENTS 6.1 After operation, the fuse assembly and the disconnector must withstand full element voltage and full voltage between the terminals of the disconnected capacitor respectively plus any unbalance voltage due to fuse or disconnector action and any short-time transient overvoltages normally experienced during the life of the capacitor. 6.2 Throughout the life of the capacitor, the disconnector shall be capable of carrying continuously a current equal to or greater than 1'1 times the maximum permissible unit current and the fuses capable of carrying continuously a current equal to or greater than the maximum permissible unit current divided by the number of paml!el fused paths. 2 to testing, measuring and safety circumstances, bs necessary to make some modifications to the under test; for example, those indicated in B ( see the different test methods given in B ). Type tests of disconnectors are performed on a capacitor unit that shall have passed all routine tests stated in IS 2834 : 1986. 8.1.2 Type tests are considered valid if they are performed on capacitors of a design identical with that of the capacitor offered, or on a capacitor of a design that does not differ from it in any way that might affect the properties .to be checked by the type test. 8.2 Routine Tests 8.2.1 No routine tests are required., IS 12672 a:1984 `9 DISCHARGE 9.1 TEST The fuses and disconnectors shall be subjected to five discharges within 10 min from a dc test voltage through a gap situated as closely as possible to the capacitor, without any additional impedance in the circuit. 9.1.1 The Table 2. "9.2 TO container, a check should be made to ensure that: a ) no significant deformation of sound fuses is apparent; and b ) not more than one additional fuse ( or one-tenth of fused elements directly in parallel ) has been damaged ( see B-1.2, Note 1 ). If method B-3 in Annex B is used, the following Note must be observed. NOTE - A small amount of blackening of the impregnant will not affect the quality of the capacitor. 10.4 Voltage Container Test After Opening the test voltage shall be taken from have shall prove that the fuses or disconnector not operated, a capacitance measurement Table 2 Test Voltages ( CIuuse 9.1.1 ) Test Voltage ( Times Unit Voltage ) (2) Rated Bank Voltage (1) Up to 650 V Above 650 V 2.0 UN 25 UN A voltage test shall be carried out by applying for 10 seconds the voltage given in Table 4 across the broken down element and the gap in its blown fuse. During the test, the gap shall be in the impregnant. No breakdown over the fuse gap is allowed. Table 4 dc Test Volta ge ( Clause Rated Bank Voltage (1) be made before and after the test. A measuring method shall be used, that is, sufficiently sensitive . to detect the capacitance change caused by one blown .fuse. 18 DISCONNECTING 10.1 Test Procedure TEST ON FUSES 10.4, and Tuble 1 ) ( Times dc Test Voltage Element Voltage (2) ) Up to 650 V 2'6 Uxe 3.5 U,e The disconnecting test on fuses is performed .at the lower voltage limit, in accordance Table 3 and then, as soon as possible after blowing of one fuse, at the upper voltage until the blowing of another fuse. 10.1.1 first with the !imit in Above 650 V Certain Annex B. test methods are indicated NOTE - For units with all elements in parallel and for all units if test procedure B-3, B-4, B-5, or B-6 indicated in Annex B is used, this test can be replaced by an ac test before the opening of the unit. The test voltage between the terminals is selected through calculations using capacitance ratio such that rhe voltage across the breakdown element and the gap in its blown fuse is the Table 4 value divided by dx 11 DISCONNECTING DISCONNECTOR 11.1 Test Procedure TEST ON Table 3 ac Test Voltages ( Clause 10.1, Rated Bank Voltage and Table 1 > ac Test Voltage ( Times Unit Voltage T--_-A_-_~ ) Lower Limit (1) Up to 650 V Above 650 V (2) 0.9 u, 0.9 UN Upper Limit (3) 1.6 U, 2'2 u, NOTE-If the test is carried out with dc, the test voltage shall be 2/2 times the corresponding ac test voltage. 10.2 Capacitance Measurement The capacitor is preheated in a chamber before applying the test voltage until all parts reach a temperature of 60°C. An ac test voltage of 1'6 UN shall be applied until the disconnector interrupts the current through the capacitor. If the disconnector does not operate within 8 h, the test voltage is raised to 1'75 UN. 11.1.1 If, after further has still not operated, finally be raised to 2 UN rupted. If no interruption rature may further be the manufacturer. After the test, capacitance shall be measured to that the fuse(s) has ( have ) blown. A measuring method shall be' used that is sufficiently sensitive to detect the capacitance change caused by one blown fuse. prove 8 h the disconnector the test voltage should until the current is interis achieved, the temperaised at the option of NOTE - Precautions shall be taken when performing this test against the possible explosion of a capacitor unit. 11.2 Capacitance Measurement 10.3 Inspection of the Unit Before opening, no significant deformation of the container shall be apparent. After opening the 3 After the test, the capacitance shall be measured to prove that the disconnector has operated. IS 12672: 1989 11.3 Inspection of the Unit Only slight traces of impregnant of the capacitor are allowed. on the outside In addition, a voltage test between terminals and container shall be made by applying for 10 seconds, the test voltage given in 1s 2834 : 1986. The test voltages shall be applied after capacitor has cooled to room temperature. No internal breakdown is allowed. NOTE - The current shall be recorded during the test.. 11.4 Voltage Tests A voltage test between terminals shall be carried out by applying for 10 seconds an ac voltage equal to 2'15 UN, or a dc voltage equal to 4.3 UN. the ANNEX GUIDE A-l FOR CO-ORDINATION A PROTECTION ( Clause 1.4 ) OF FUSE AND DISCONNECTOR GENERAL A-l.6 In Fig. 2, the operational principle of the internal overpressure disconnector is given. A-l.7 Because of the self-healing properties of the capacitor, breakdowns are not dangerous and But, in do not increase the current significantly. the event of rising pressure ( for example, caused by thermal instability which may occur at the end of the life of the capacitor, or in some cases, by an excessive number of self-healing breakdowns, caused by extreme overloads), the self-healing power capacitor should be protected by an internal overpressure disconnector. A-l.1 The fuse is connected in series with the element that the fuse is designed to isolate if the element becomes faulty. After the breakdown of an element, the fuse connected to it will blow and isolate it from the remaining part of the capacitor which allows the unit to continue in service. The blowing of one or more fuses will cause voltage changes within the bank. A-l.2 The voltage across sound unit(s) must not exceed the value given in the relevant standard ( IS 2834 : 1986 ). A-2 PROTECTION A-2.1 The protection operate selectively. SEQUENCE of a capacitor bank must A-l.3 Depending on the internal connection of the units, the blowing of one or more fuses may also cause a change of voltage within the unit. A-l.4 The remaining elements in a series group will have an increased working voltage and the manufacturer of capacitor shall, on request, give details of the voltage rise caused by the blown fuses. A-1.5 A typical arrangement of internal overpressure disconnectors in a three-phase unit is given in Fig. 1. A-2.2 The first step is the fusing of the element(s) or the operation of the disconnection. A-2.3 The second step is the relay protection of the bank ( for example, overcurrent or unbalance protection ). A-2.4 The third step is the network or the protection. plant FIG. 1 TYPICALLAY-CUT OF A THREE-PHASE DELTA-CONNECTED CAPACITOR UNIT, WITH Two INTERNALOVERPRESURE DISCONNECTORS ( D1 AND D, ) * 4 IS 12672: 1989 NOTES 1 Depending on the output of the bank, the design of the relay protection, etc, all the three steps are not necessarlly~used in all capacitor banks. 2 In large banks, an alarm stage may also be used. 3 Unless the fuse alwaysMows as a result of discharge energy within the voltage range in 5 1, the manufacturer shall provide the current/time characteristic and tolerance of the fuse. RESILIENT CASE IL--LINE 2A Disconnector Before Operation 28 Disconnector After Operation NOTE -In the event of rising pressure, a resilient wall of the container bulges out. By movement of the pull strap, the notched copper strip is torn into two sections. By the action of the tension spring, the current is interrupted and the arc is extinguished very quickly, because the disconnector is installed in an oilfilled insulating tube. FIG. 2 PRINCIPAL OF DESIGN FOR AN OVERPRESSURE DISCONNECTOR FOR SELF- HEALING MEDIUM VOLTAGE POWER CAPACITORS ANNEX B [ Clauses 8.1, 10.1.1, 10.3( b ), and Table 4 TEST PROCEDURES B-l B-l.1 ~-6, 1 FUSES FOR THE DISCONNECTING given in B-2 to method, shall be TEST ON INTERNAL GENERAL or One of the test procedures an agreed alternative used. B-1.2 choice NOTES 1 At the upper voltage limit, one additional fuse ( or one-tenth of the fused elements directly in parallel ) connected to a sound element(s) is allowed to be damaged. If no agreement has been reached, the is left to the manufacturer ( SW also Note 3 under 8.1 1. 2 The test voltage shall be maintained for some seconds after a breakdown, to ensure that the fuse has disconnected correctly, unaided by disccnreclion of the power supply. I& 12672 : 1989 3 In special cases, it may be necessary to extend the testsuntil twoor morebreakdowns of capacitor elements have occurred. The number of breakdowns at each voltage limit shall in such cases be subject toaareement between the manufacturer and the p&chaser. If. the number of breakdowns is exceeded, the voltages stated in 10 4 may have to be increased. 4 To verifv the current limiting behaviour of the fuses when tested at the upper voltage limit, the voltage drop excluding transient, across the blown fuse must not exceed 30 percent. 5 If the fuse does not precautions must be parallel stored energy current available from service conditions. fulfil the requirements of Note 4 taken to make certain that the and the power-frequency fault the system are representative of the satisfacconnected, tainer. permanently or during the test, to the confor capacitors having 3 dc voltage is specially suitable all elements in parallel. B-4 ELECTRICAL BREAKDOWN ELEMENT ( FIRST SOLUTION ) OF THE B-4.1 Some elements in the test unit are each provided with, for example, a tab, inserted between the dielectric layers. Each tab is connected to a separate terminal. B-4.2 The test voltage may be ac or dc, the choice being left to the manufacturer. B-4.3 To obtain the breakdown of an element thus equipped, a surge voltage of sufficient amplitude is applied between tab and one of the foils of the modified element. B-4.4 In the case of ac voltage, the surge must be triggered at the instant of the peak or very near to it. B-4.5 Capacitor current is to be recorded the test. B-5 ELECTRICAL BREAKDOWN ELEMENT ( SECOND SOLUTION OF ) A test shall then be made to demonstrate tory operation of the fuse. 6 Precautions shall be taken when performing this test against the possible explosion of a capacitor unit and the explosive projection of the nail. B-2 CAPACITOR PREHEATING B-2.1 The capacitor unit is preheated in a chamber before app1yir.g the ac test voltage at the lower limit. Preheating temperature ( 100 to 150" C ) is chosen by the manufacturer to achieve a practical short time ( a few minutes to a few hours ) to the first breakdown. during THE temperature should be used when aonlvine; the test voltage at the higher voltage limit'io-avoid breakdowns- before reaching the test voltage. B-2.3 Capacitor current is to be recorded the test. during B-2.2 A lower preheating B-5.1 Some elements in the test unit are each provided with, for example, a short fuse wire connected to two extra tabs and inserted between the dielectric layers. Each tab is connected to its own bushing. B-5.2 The test voltage may be dc or ac, the choice being left to the manufacturer. B-5.3 To obtain breakdown of an element equipped with this short fuse wire, a capacitor charged at a sufficient voltage is connected to the two bushings connected to it in order to explode the wire. B-5.4 In the case of ac voltage, the connection of the charged capacitor causing the wire explosion must be triggered at the instant of the peak voltage or very near to it. B-5.5 Capacitor current is to be recorded the test. ELEMENT NOTE - To prevent excessive internal liquid pressure . . due to high temperature, the unit may be equlppea with a relief tube including a valve which must be closed at the instant of applying the test voltage. B-3 MECHANICAL ELEMENT B-3.1 Mechanical PUNCTURE OF THE puncture of made by a nail which is forced through a pre-drilled hole in the test voltage may be dc or ac, the to the manufacturer. the element is into the element container. The choice being left during THE B-3.2 If ac voltage is used, capacitor current is to be recorded during the test and the timing of puncture is to be done to ascertain that the breakdown is triggered to take place at the instant of the peak of the ac test voltage, or very near to it. NOTES 1 Puncture of only one element cannot be guaranteed. B-6 ELECTRICAL ( THIRD BREAKDOWN SOLUTION ) OF ( or some elements ) in a unit is at the time of manufacture removed and replaced with a weaker dielectric. B-6.1 A small part of an element For example : 10 to 20 cm2 of a film-paper-film dielectric is punched away and the hole is covered with two thin papers. This method will require experience on how to make a suitable dielectric strength redpction. 6 2 In order to limit the possibility of a flashover to the container along the nail, or through the hole caused by thelnail, the punctures may be performed in the elements Standard Mark The use of the Standard Mark is governed by the provisions of the Bureau of Indian Act, 1986 and the Rules and Regulations made thereunder. The Standard Mark on products covered by an Indian Standard conveys the assurance that they have been produced to comply with the requirements of that standard under a well defined system of inspection, testing and quality control which is devised and supervised by BIS and operated by the producer. Standard marked products are also continuously checked by BIS for conformity to that standard as a further safeguard. Details of conditions under which a licence for the use of the Standard Mark may be granted to manufacturers or producers may be obtained from the Bureau of Indian Standards. * Standards Bureau of Indian Standards BIS is a statutory institution established under the Bureau of In&n Standards Act, 1986 to promote harmonious development of the activities of standardization, marking and quality certification of goods and attending to connected matters in the country. Copyright BIS has the copyright of all its publications. No part of these publications may be reproduced in any form without the prior permission in writing of BIS. This does not preclude the free use, in the course of implementing the standard, of necessary details, such as symbols and sizes, type or Enquiries relating to copyright be addressed to the Director (Publications), BIS. grade designations. Rev&Ivy q:.r a$ krdian Standards Star&lards are review&$ periodically and revised, when necessary and amendments, if any, are issued from time to tim&:`:$&ers of Indian Standards should ascertain that they are in possession of the latest amendments or -on. Comments on this Indian Standard may be sent to BIS giving the following reference : Indian Dot : No. ETDC 29 ( 2978 ) Amendments Issued Since Publication Amend No. Date of Issue Text Affected BUREAU Headquarters: OF INDIAN STANDARDS Manak Bhavan, 9 Bahadur Shah Zafar Marg, New Delhi 110002 Telephones: 331 01 31, 331 13 75 Regional Offices: Central : Manak Bhavan, 9 Bahadur Shah Zafar Marg NEW DELHI 110002 Eastern : l/14 C. I. T. Scheme VH M, V. 1. P. Road, Maniktola CALCUTTA 700054 Northern : SC0 445-446, Sector 35-C, CHANDlGARH 160036 Telegrams : Manaksanstha (Common to all Offices) Telephone 331 01 31 t 331 13 75 36 24 99 2 1843 { 3 16 41 Southern : C. 1. T. Campus, IV Cross Road, MADRAS 600113 Western : Manakalaya, E9 MIDC, Marol, Andheri (East) BOMBAY 400093 Branches : AHMADABAD. BANGALORE. BHOPAL. BHUBANESWAR. GUWAHATI. HYDERABAD. JAIPUR. KANPUR. PATNA. TRIVANDRUM. Printed at Saini &inters, Delhi, India 6 32 92 95